Cooling electric machinery



I 4 1,631,765 Jufle 1927' R. RUDENBERG coonme ELECTRIC MACHINERY Filed Auz. 25, 1921 Patented June 7,1927.

UNITED STATES PATENT OFFICE.

REZNHGLD RUDENIBERG, OF BERLIN-CHARLOTTENBURG, GERMANY, ASSIGNOR TO SIEMENS-SCHUCKEBTW'ERKE GESELLSCHAFT MIT BESCEEANKTER HAFT'U'ITG, OF SIEMENESTADT, IIEAR BERLIN, GERMANY, A CORPORATION OF GERMANY.

COOLING ELECTRIC MACHINERY.

Application filed August 23, 1921, Serial No. 494,546, and in Germany October 7, 1918.

(GREKNTED UNDER THE PROVISIONS 01 THE ACT 01 MARCH 3, 1921, 41 STAT. L, 1313.)

(i. e. power driven) ventilation for cooling purposes, whichmust be of sufiicient dimen- 10 sions to suiiice for the maximum continuous output required. This positive ventilation is usually embodied in the machine casing in the form of fan blades mounted in well known manner on the machine shaft.

Arrangements are also known for automatically controlling the supply of cooling air to a dynamo-electric machine by means of a thermostatic device aii'ected by the temperature of the machine so as to give a supply appropriate to the needs of the latter.

in many cases however, the maxin'uun load or output just referred to occurs (tor example in central stations) only during a tow hours of the day, and at that perhaps only during a few winter months, and there tore the machinery is underloaded or only imperfectly utilized at all other times.

This imperfect utilization of the machinery is obviated according to the invention, by running the machinery normally up to a load at which it reaches the permissible limit of temperature, the case of extreme output being provided for by a supplementary or extraneous ventilation added to the ordinary normal ventilation.

This extraneous ventilation is produced by external fans or ventilators and conveyed to the machine.

Thus as regards the utilization of the machines, similar conditions prevail in working as exist for example in case of steam turbines, which are fully loaded for econoinical utilization in the normal working, and to which fresh or live steam may be supplied for extreme outputs, thereby attaining a. larger output, although with a lesser degree of ei'liciency.

Particularly favourable conditionsare ob tained for the mixed ventilation, which is employed for the extreme output, it the air pressure of the ordinary or main ventilator v(when co-operating with the auxiliary ventilater) is kept constant between the normal output and the extreme output.

In order that the invention may be clearly understood and readily carried into effect reference will now be had by way of example to the accompanying diagrammatic drawings in which Fig. 1 illustrates an arrangement having an auxiliary additional air-supply with the ordinary supply, and

in series Fig. 2 represents the characteristic curve diagram.

In Fig. 1, m indicates a dynamo-electric machine, which is provided internall y with a main tan or normal ventilating arrangement.

This normal, internal ventilating arrangement may constitute any of the many well known types of ventilation for this machines, being operated by the ma class of chine itself, and the illustration thereof has been omitted in the drawings as fully within the knowledge of those skilled in the art.

eis

the inlet and u is the outlet for the cooling air. 7 is an auxiliary tan or ventilator which has an inlet 25 and an outlet 1'. This auxiliary tan may be driven by any suitable outside means known in the art and is, therefore, indicated in the drawings merely symbolically by a pulley h and belt is.

of air necessary under the extreme output.

This danger can be avoided according to the invention by making the ordinary ventilator of a size which is adequate to pass the increased quantity of air through the machine. acterlstic curve, (that is to say the This will be the case it its charrelationship of the air pressure to the quantity of of alr) is level or approximately so for the conditions under consideration.

The diagram in Figure 2 will serve to ex plain this. The curve G shows the necessary air-pressure to be applied in relation to the quantity of cooling air Q, flowing through the generator, such pressure increasing approximately with the square in relati quantities of air.

on to the The curve V is the characteristic for the main or normal ventilator; it shows the relationship-between the pressure and the quantity of air which passes through the ventilator.

The point that. which the two curves intersect, corresponds to the normal working point, at which the main or primary ventilator acting against the resistance of the airpath forces the requisite quantity Q of air through the machine, viz, the quantity of air which exactly sufiices for cooling the machine at-normal load.

If it be desiredto force a smaller quantity of airthrough-the machine, the pressure- (which corresponds to the di'tlerence ot the curves 1V. and G) must of course be reduced; On the other hand it, as in the present case, it be desired to force larger. quantities (for example Q through the machine, theauxiliary' ventilator must deliver the air with the-effectivepressure P;- correspondingflto the di'fl'erence GV.

Now suppose that in order to keep themachine below the temperature limit in the case of extreme load or output, a quantity of cooling air Q, is necessary. In order to force this quantity through the machine, the pressure 1),, must. be applied and this pressure canbe made up of a pressure p due to the primary ventilator and a pressure 1); due to the auxiliary ventilator.

In order however that the. arrangement may WOI'k economically, it is necessary that under these new conditions, the ordinary or.

primary ventilator should deliverits quantity of air approximately under its previous or maximum pressure, whilst the additional ventilation mustmalre up the difference between p and the pressure (which will not exceed 1) yielded by the ordinary ventilator. This is obtained, with series connection of the ventilators, if 19,, 12, cuts the characteristic V at or near its flat part or highest level.

F or the additional extraneous ventilation according to the invention, it is necessary that the ordinary ventilator should he of such size, at the outset, that with the series connection described it can transmit a larger amount of air without too great a drop in pressure.

I would state that. I am aware that arrangements for controlling the temperature of oyuamo electric machinery either automatically or thermostatically have been proposed hetore, and'I do not claim such per se.

I claim In dynamo-electric machines in combination, itself-ventilator directly mounted on the shaft of the machine and adapted to furnish ventilation for normal load only, and a separately driven ventilator connected in series with said self-ventilator for sup plying ventilation at excess machine load, said selt-veriilator being of suclrconstruction thatthe pressure drop therein is approximately the same for the passage of the quantity of air required at normal load, as for the passage of the quantity of air required at overload.

In testimony whereot'laffix my signature.

REINHOLD RUDENBERG. 

